A hazard traditionally associated with outdoor activities such as hiking and camping has been the possibility of exposure to poison ivy, poison oak, poison sumac and the like, which plants are in the rhus toxicodendron family. The sap of such plants contains a toxin which can cause an allergic reaction upon contact with the skin, despite the fact that the toxic substance naturally occurs in low concentrations (e.g., 2-5% of the sap) and the contact is usually brief and incidental. The extent of reaction varies from individual to individual. Some individuals may experience little or no reaction or simply some itching which disappears after a few days, while other develop a severe skin rash which may require treatment with antibiotics and may need several weeks or even months fully to heal. Unfortunately, one typically does not realize he has been exposed to poison ivy and the like until the symptoms develop some time after contact.
The most common approach to this problem has been to avoid any contact with such plants, which approach is extremely practical but not always workable under the circumstances. The leaves of poison ivy, for example, are similar to the foliage of other harmless plants and thus may not be readily distinguishable. Various medications are available for treating the effects of contact with these plants. In addition, techniques like that disclosed in U.S. Pat. No. 2,451,955 have been developed for determining in advance the sensitivity of individuals to poison ivy and the like.
Although the benefits of early treatment have been widely appreciated, little effort has been expended heretofore in developing a technique by which an individual would be promptly alerted to his having just contacted poison ivy, poison oak, poison sumac or the like. Early realization of such contact would enable an individual to wash the affected area and/or apply suitable medication, thereby limiting spread of any rash, shortening its duration and otherwise minimizing the allergic reaction.